Electron-transfer pathways ruthenium complex

Ruthenium catalysts found many applications in C-C bond formation reactions (selected reviews [157-161]). Ruthenium occurs mostly in oxidation states +2 and +3, but lower as well as higher oxidation states can easily be reached. Thus ruthenium compounds are frequently used in oxidative transformations proceeding by either single or two electron transfer pathways (selected reviews [162-164]). It has long been known that ruthenium complexes can be used for the photoactivation of organic molecules (selected reviews [165, 166]). Ruthenium complexes are applied as catalysts in controlled or living radical polymerizations [167-169]. 

Figure 11 Molecular model of the complex between Ru-65-cyt i>5 and Cc. The geometry of the complex is the same as that of the complex involving native cytochrome proposed by Salemme. The heme groups (red), and the ruthenium complex (green) are highlighted. The atoms forming an electron-transfer pathway between the ruthenium complex and the heme group of Ru-65-cyt hs are colored yeUow. The lysine and arginine residues are blue, while aspartate and glutamate residues are red ...

A number of mechanistic pathways have been identified for the oxidation, such as O-atom transfer to sulfides, electrophilic attack on phenols, hydride transfer from alcohols, and proton-coupled electron transfer from hydroquinone. Some kinetic studies indicate that the rate-determining step involves preassociation of the substrate with the catalyst.507,508 The electrocatalytic properties of polypyridyl oxo-ruthenium complexes have been also applied with success to DNA cleavage509,5 and sugar oxidation.511... 

Ruthenium, osmium, and rheitium complexes have been used to define electron-transfer rates over defined distances and pathways see Iron Heme Proteins Electron Transport, Long-range Electron Transfer in Biology) They can be attached to external His residues by displacement of its... 

Issues related to the preferred pathways and the distance dependence of electron transfer in biological systems have been addressed by covalently linking electron-transfer donors or acceptors (e.g. a ruthenium complex) to specific sites (e.g. a histidine) of a protein or an enzyme.The distance dependence of the electron-transfer rate constants is generally fitted to equation (44), with most values of for proteins falling in the range of 1.0 to 1.3 A The protein in... 

The interprotein electron-transfer reactions of Ru-65-cyt bs can be studied using a sacrificial electron donor such as aniline to reduce Ru(III) and prevent the back reaction k2, as described in Scheme 2. Appropriate sacrificial electron donors can also reduce Ru(IB) to Ru(I), which then reduces Fe(III) as shown in the top pathway of Scheme 2. Cyt b is rapidly reduced by either pathway, and is then poised to transfer an electron to another protein. The reaction of cyt bs with Cc using this methodology will be described in the next section. Covalent labelling of Cc with ruthenium complexes and subsequent flash photolysis has provided a... 

After having observed that the most active ruthenium-based catalyst systems for olefin metathesis also displayed a high efficiency in atom transfer radical polymerisation, we then became interested in comparing the role of the catalyst in those two different reaction pathways. Ruthenium alkylidene complexes 4-6 are unsaturated 16-electron species which formally allow carbon-halogen bond activation to form a 17-electron ruthenium(III) intermediate. Our preliminary results indicate that polymerisations occur through a pathway in which both tricyclohexylphosphine and/or imidazolin-2-ylidene ligands remain bound to the metal centre. 

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